Design And Performance Study Of Silicomanganese Slag-Limestone Low Clinker Cementitious Material System

With the rapid development of China’s economy,the demand for cement is increasing,while the consumption of resources and energy and CO₂emissons are all further increased.Developing of the low clinker and high grade cementitious materials by industrial solid wastes has become one of the most effective ways to reach the carbon peak of cement industry,which proposes many more requirements for cement admixture properties and the synergy of multiple admixtures.Silicomanganese slag is an industrial waste with high yield and certain potential activity,while limestone is an inexpensive and easily available natural mineral in Sichuan.The composite of silicomanganese slag and limestone was thus designed and prepared to produce the low-carbon and low-clinker cement in this study,which was applied to prepare C30 grade concrete.Results are as follows:（1）Silicomanganese slag powder has better water reducing effect,it can reduce the water requirement for standard consistency of the cement.Setting time of the silicomanganese slag-clinker cementitious material is prolonged with the increase of admixture,the early compressive strength of cement mortars decreases obviously while the later mechanical properties developed rapidly,the 56 d compressive strength of the mortar by using the cement with 30%of silicomanganese slag powder is close to that of P.I cement group.Silicomanganese slag accelerates the early hydration of clinker and slows down the early hydration heat of cement.（2）Setting time of the limestone-clinker cementitious material is shortened.The initial and final setting time of the cement with 20%of limestone powders is shortened by 31 min and42 min,respectively,compared to that of P.I cement.The excessive amount of limestone in cement is not conducive to the development of later mechanical properties.The early hydration rate and hydration heat of the cement are all increased through the nucleation-inducing effect of limestone powder.（3）The incorporation of limestone powder can reduce the effect of silicomanganese slag on the setting time and early mechanical properties of silicomanganese slag-limestone-clinker cementitious material system.It is conducive to the improvement of cement workability and mechanical properties,especially,the early mechanical properties of the silicomanganese slag-limestone-clinker cementitious material is better than that of the silicomanganese slag-clinker system.Nucleation-induced hydration effect of the limestone powder and later hydration of silicomanganese slag promote the early hydration and ensure the rapid development of the composite cementitious material.Silicomanganese slag powder and limestone powder synergistically participates in the hydration process,thus increases the total amount of hydration products and compacts the microstructure of the hardened slurry.（4）Silicomanganese slag-limestone-clinker cementitious material is used to preoare concrete.The cement has little effect on the workability of the concrete,but would significantly decreased the early strength of the concrete.The early mechanical properties of the concrete is improved after the addition of limestone powder in cement.The compressive strength of concrete by using the cement with 5%of limestone powders is reached maximum,and the 3 d and 7 d compressive strength of the concrete increases,the56 d and 90 d compressive strength approach to that of concrete by using P.I cement.The frost resistance,carbonation resistance and shrinkage behavior of concrete specimens prepared by silicomanganese slag-limestone-clinker cementitious material in the range of small amount of limestone powder would be improved.